An ultrasonic transducer transmits and receives an ultrasonic wave and diagnoses a tumor inside a body for example.
Although most of ultrasonic transducers have used the vibration of a piezoelectric body so far, recent advances in the MEMS technique opened up the possibility of using a cMUT (Capacitive Micromachined Ultrasonic Transducer) having a diaphragm formed on a silicon substrate.
For example, U.S. Pat. No. 6,320,239B1 discloses a cell of cMUTs and a CMUT array.
In addition, U.S. Pat. Nos. 6,571,445B2 and 6,562,650B2 disclose techniques for forming cMUT cells on the top of a signal processing circuit built on a silicon substrate.
Moreover, according to 2004 IEEE Ultrasonics Symposium, pp. 2223-2226, a cMUT cell includes a compliant support structure formed on a lower electrode.